Dolby 5.1 in MKVs (and AC3) plays as stereo on Android TV

Description

I use MKV files with embedded audio. The stereo ones play OK in VLC, but Dolby 5.1 just plays as stereo. I'm unsure whether this is a problem with the TV or not. Should I be contacting Philips as well?

Expected behavior

VLC should handle 5.1 audio

Actual behavior

I have a 5.1 test AC3, just audio, which speaks the names of the channels. I find that most of the channels appear in more than one speaker. Effectively, it's stereo but makes use of the rear speakers (but they are carrying the same audio as the front ones - there's no separation). I've also played test videos downloaded from the web, and I can tell that the surround isn't working. Kodi, and the built-in Android TV player app, both play them with surround and there's a clear difference.

Context

App version

3.5.2

Android version

TPM191E_R.101.002.178.000 Philips/PH9M_EA_5599

Device model

PHILIPS TV 43PUS8545/12 LED TV

App mode

TV